This application is related to Japanese Patent Application No. 2001-213917 filed on Jul. 13, 2001, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a photovoltaic module. More specifically, it relates to a photovoltaic module capable of withstanding harsh environments such as volcanic areas, hot spring areas and water purification and sewage treatment facilities.
2. Description of Related Art
Photovoltaic modules utilized in a residential photovoltaic power generation system and an independent power source system are required to have long-term reliability.
Therefore, mostly utilized is a photovoltaic module of a super-straight structure composed of a sealing polymer layer (ethylene-vinylacetate copolymer: EVA) on the light receiving surface side, a photovoltaic cell, a sealing polymer layer (EVA) on the rear surface side and a weatherproof film for sealing the rear surface side which are stacked in this order on a light receiving glass and integrated by lamination (see, for example, Japanese Unexamined Patent Publication No. Hei 10 (1998)-256580).
In connection with the widespread use of the residential photovoltaic modules, industrial photovoltaic modules are also coming into wide use for buildings, warehouses, gymnasiums and public buildings of large capacity.
Features of the industrial photovoltaic module are that it generates as large power as 10 kW or more in comparison with 3 kW of the residential photovoltaic module and occupies a larger area. Further, the industrial photovoltaic module is installed in harsh outdoor environments, e.g., areas suffering from salt damage such as at seaside and at sea, areas exposed to sulfide gas such as volcanic areas and hot spring areas and places exposed to chlorine gas or sulfide gas such as water purification and sewage treatment facilities, and therefore it needs to be resistant against such environments.
For the photovoltaic module installed in the salt damage area, measures against electrolytic corrosion are taken.
The object of taking such measures is to prevent the electrolytic corrosion caused by adhesion of salt contained in the sea breeze to a gap between a frame which constitutes the photovoltaic module (generally an aluminum frame) and a tapping screw which secures the frame (generally made of stainless steel).
More specifically, a nonmetal insulating washer is fitted to the tapping screw and then the frame is secured with the tapping screw. Then, an exposed surface of the screw is sealed with a silicon polymer, a section of the frame is anodized to prevent contact with outside air and the gap between the frame and the photovoltaic module is filled with a silicon polymer. Then, the photovoltaic module is fixed to a steel pedestal with a bolt fitted with a nonmetal insulating washer. Thus, the electrolytic corrosion is prevented. This technique has been widely accepted in the market.
The above-mentioned measures against the electrolytic corrosion are solely directed to the photovoltaic module installed at seaside or at sea, and not to the one installed in the area exposed to sulfide gas or chlorine gas such as volcanic areas, hot spring areas and water purification and sewage treatment facilities.
In order to install the photovoltaic module in the volcanic areas or hot spring areas, measures should be taken to cope with the exposure to poisonous gases such as hydrogen sulfide gas (H2S) and chlorine gas (Cl2).
Further, in the water purification and sewage treatment facilities, measures should be taken against the exposure to poisonous gases such as hydrogen sulfide gas (H2S), chlorine gas (Cl2), methylmercaptan (CM3SH), methyl sulfide ((CH3)2S) and ammonia (NH3).
In the ordinary photovoltaic modules including the above-mentioned one which is manufactured in view of the salt damage, a PET film is generally utilized as a rear surface sealing weatherproof film.
However, the weatherproof film which is solely made of PET allows vapor to permeate. The vapor permeated through the PET film also penetrates a rear surface sealing polymer layer (EVA layer) to deteriorate the characteristics of the photovoltaic cell.
Therefore, also utilized is a rear surface sealing weatherproof film of a three-layer structure in which a metal layer or an inorganic oxide layer is sandwiched between the PET films (see, for example, Japanese Unexamined Patent Publication No 2001-257372).
That is, the metal layer or the inorganic oxide layer which does not allow the vapor permeation is provided as a moisture-proof layer and the PET films are formed to sandwich the moisture-proof layer. This three-layer structure enhances vapor impermeability of the rear surface sealing weatherproof film.
However, the PET film includes an ester bond in its structure. Therefore, if the PET film is exposed to a complex environment in which poisonous gases such as hydrogen sulfide gas, chlorine gas, methylmercaptan, methyl sulfide and ammonia exist together or these gases and vapor are mixed, hydrolysis reaction occurs to increase carboxylic acid groups in the ester bond. This deteriorates the PET film and finally decreases the mechanical strength of the film, thereby the film may be exfoliated or cracked.
When the PET film is exfoliated or cracked, the moisture-proof function of the rear surface sealing weatherproof film is considerably impaired as a matter of course, which results in the deterioration of the characteristics of the photovoltaic module.
Therefore, in order to install the photovoltaic module in the volcanic areas, hot spring areas and water purification and sewage treatment facilities, measures should be taken against the exposure to the above-mentioned poisonous gases.
Under the above-mentioned circumstances, the present invention has been achieved to provide a photovoltaic module which can be used without any characteristic deterioration even if it is installed in a place exposed to poisonous gases such as hydrogen sulfide gas, chlorine gas, methylmercaptan, methyl sulfide and ammonia.
In another aspect, the photovoltaic module according to the present invention allows the installation of the photovoltaic module in harsh outdoor environments that have been given a wide berth, for example, volcanic areas, hot spring areas and water purification and sewage treatment facilities, thereby contributing to the dissemination of the photovoltaic module and increasing an industrial demand thereof.
The present invention provides a photovoltaic module comprising: a light-transmissive substrate; a first sealing polymer layer stacked on the substrate; a photovoltaic cell stacked-on the first sealing polymer layer; a second sealing polymer layer stacked on the photovoltaic cell and a weatherproof film stacked on the second sealing polymer layer, wherein the weatherproof film includes a moisture-proof layer provided on the second sealing polymer layer and a gas-proof layer provided on the moisture-proof layer, the gas-proof layer being made of polyphenylene sulfide.
Specifically, the photovoltaic module according to the present invention includes, as an outermost layer of the weatherproof film, a polyphenylene sulfide (PPS) layer having excellent resistance against hydrogen sulfide gas, chlorine gas, methylmercaptan, methyl sulfide and ammonia that are generated in the volcanic areas, hot spring areas and water purification and sewage treatment facilities. This structure prevents the deterioration of the moisture-proof layer formed below the gas-proof layer.
As a result, the present invention provides a photovoltaic module which can be used without any characteristic deterioration even if it is installed in a place exposed to the above-mentioned poisonous gases or these gases and vapor.